In a joint statement, they said Riyadh's explanation - that the dissident journalist was killed when an argument spiralled out of control - needed "to be backed by facts" amid growing scepticism about the Saudi version of events.

Meanwhile a senior official in Riyadh said Khashoggi's body had been smuggled from the consulate wrapped in a rug even as Saudi Arabia’s foreign minister appeared on American TV to claim authorities still did not know exactly how the 59-year-old died or where his body was.

In the joint statement Jeremy Hunt, the Foreign Secretary, Jean-Yves Le Drian, his French counterpart, and Germany's Heiko Maas condemned the killing.

“Yet there remains an urgent need for clarification of exactly what happened on October 2 - beyond the hypotheses that have been raised so far in the Saudi investigation, which need to be backed by facts to be considered credible,” they said.

Donald Trump initially said he found the Saudi account to be credible before rowing back on SundayCredit: Jonathan Ernst/Reuters

The three demanded proper accountability and due process for any crimes committed.

“We will ultimately make our judgement based on the credibility of the further explanation we receive about what happened and our confidence that such a shameful event cannot and will not ever be repeated,” they said.

A Saudi official, speaking anonymously to Reuters, offered more details about what might have happened inside the consulate.

He said a team of 15 Saudi nationals sent to confront Mr Khashoggi threatened him with being drugged and kidnapped, and taken to a safe house in Istanbul for questioning. He was killed in a chokehold when he resisted.

His body was then smuggled out of the building wrapped in a rug while a member of staff dressed in Mr Khashoggi's clothes to make it appear as if he had strolled out of the consulate.

Yet in an interview on Fox News, Adel al-Jubeir, the Saudi foreign minister, said it was unclear what had happened as he offered his condolences to Mr Khashoggi’s family.

“He was killed in the consulate. We don’t know in terms of details how. We don’t know where the body is,” he said. “We are determined to uncover every stone… We are determined to punish those who are responsible for this murder.”

Late on Sunday, the Saudi Press Agency said both Saudi King Salman and Prince Mohammed had called Mr Khashoggi's son, Salah, to express condolences.

“There were not people closely tied to him,” he said. “This was an operation that was a rogue operation.”

For two weeks, Saudi officials claimed Mr Khashoggi had left the embassy safely. But a drip-feed of information from Turkish security sources painted a horrifying tableau of premeditated murder carried out by a hit squad who flew in from Riyadh with a bone saw.

Turkey is said to hold recordings of what happened in the consulate.

Mr Erdogan told a rally on Sunday: "We are looking for justice here and this will be revealed in all its naked truth, not through some ordinary steps but in all its naked truth." He is expected to make a full statement on Tuesday.

The Turkish president and US President Donald Trump spoke on the telephone and agreed that "all aspects" of the case needed to be cleared up, Turkey's Anadolu agency said early on Monday.

Protesters accuse Donald Trump of being too close to Saudi leadersCredit: Jim Watson/AFP

Boris Johnson, the former Foreign Secretary, said the Saudi state had copied the playbook of Vladimir Putin and his efforts to silence critics, such as the attempted killing of Sergei and Yulia Skripal in Salisbury.

And he added that the UK and US must take the lead in holding Riyadh to account.

“The body must be produced,” he said. “The audio tape of the killing said to be held by the Turkish authorities – if it exists – should be made public.”

Mr Trump also toughened his line on Saudi Arabia, accusing Riyadh of lies and deception.

The US president initially said the official Saudi account – that the dissident journalist was killed in a “fistfight” - was credible.

But amid growing world outrage and pressure from within his own party to hold Saudi authorities to account, he told The Washington Post: “Obviously there's been deception, there's been lies.”

He also defended the kingdom as an “incredible ally” and returned to the possibility that the Saudi crown prince did not order his agents to kill a troublesome critic.

“Nobody has told me he’s responsible. Nobody has told me he’s not responsible. We haven’t reached that point. . . I would love if he wasn’t responsible,” he said.

His words illustrate a dilemma for the US, which sees Riyadh as a customer for billions of dollars of arms and an ally in its effort to contain Iran.

While government ministers and investors from all around the world have withdrawn from the Future Investment Initiative – known as Davos in the desert - on Sunday it emerged that Steven Mnuchin, Mr Trump’s treasury secretary, would travel to Riyadh this week to discuss the campaign against Iran.